I'm sure this has been done before, but I thought I would provide it for our community.

I made a quick, simple spreadsheet for making the calculations to plot points on compressor maps. Keep in mind these sorts of things are only for estimation purposes, but they can also be useful for showing how changes/improvements will affect your turbo system. The maths I used can be found in the Turbo Tech link in my signature.

I'm sure someone with more knowledge will chime in, but making the spreadsheet has raised a couple of questions for me. I have to run to class now, but I'll bring them up. I hope Yoshi or Tony will be able to chime in and give me some answers (or tell me what's wrong with the spreadsheet).

Okay, I made a couple changes to the spreadsheet (made VE a variable, changed some wording, etc.).

I plan to add a couple more tools to the spreadsheet. I'd like to add formulas for turbocharger outlet temperature, maybe some kind of charge cooler calculator/estimator (if I can get my hands on the necessary information), and a gear calculator. If anyone has any other ideas, let me know!

I had a spread sheet a while ago for wheel speed with tire size/gear ratio/trans in play. I wish I could find it. Might have to remake it. Your spread sheet works. Would be nicer if it plotted. But there's already like 20 things that do this on the internet.

M20_fever wrote:+1 to plotting the results. Also would be nice to see hiw egt factors in. Nice work though.

I'm not sure I understand where the results would get plotted..?

I'm looking into setting it up so all the variables were inter-related (e.g. how a drop in intake temps might increase horsepower).

How does EGT factor in, aside from affecting exhaust gas velocity (spool-up time)? I'm sure it plays a part in turbo outlet temp (which impacts intake temp, obviously). That will come in V2!

Oh, BTW, yes all of the info is available online; I just like the simple availability of setting it up in a spreadsheet. As I expand this, I'll have a little 'toolkit' available on my tuning laptop, regardless of internet connection.

Thanks for all the tips! I'll do my best to apply them. Next step is expanding the gas temperature formulas. The next sheet I'll add is the gearing calc. That should be really easy.

egt is an indicator of backpressure, which directly effects output at any given boost level. in your spreadsheet boost increases as desired HP is increased, but its not accounting for having to maintain or reduce backpressure. An engine is just an air pump right? So you need to show a metric for volume of air exiting the pump as well as air being fed into the pump, which is usually shown as exhaust temp. The plot I would expect to see would be a graph with different lines for your different output values that would highlight the balance of variable combinations.

I'm no expert by any means. My company has a guy that just does thermal ratings. It can get very deep, which is why we have to make some assumptions and generalizations. I believe there are equations to find the ratio between backpressure and exhaust temps though. I think it would be very similar to figuring intake temps after the compressor since exhaust is basically just air that is being compressed due to exhaust flow restrictions. Obviously the exhaust air is starting at a higher temp than the ambiant air at the intake, but effect is fundamentally the same. How this works into the combination of equations on your spreadsheet I have no idea, thats above my pay grade!

M20_fever wrote:I'm no expert by any means. My company has a guy that just does thermal ratings. It can get very deep, which is why we have to make some assumptions and generalizations. I believe there are equations to find the ratio between backpressure and exhaust temps though. I think it would be very similar to figuring intake temps after the compressor since exhaust is basically just air that is being compressed due to exhaust flow restrictions. Obviously the exhaust air is starting at a higher temp than the ambiant air at the intake, but effect is fundamentally the same. How this works into the combination of equations on your spreadsheet I have no idea, thats above my pay grade!

Gotcha - it's definitely a good idea to include. I'll add it to my list, but it's a ways off...